Drink dispensers are well known and are used to dispense beverages for service to customers by mixing beverage concentrates with diluents in selected ratios. The beverage concentrates may be flavored concentrate syrups, such as cola syrups, that are mixed with suitable diluents, usually carbonated or plain water, to produce a beverage.
Increasing health awareness has given rise to consumer desires for drinks that provide nutrient valve, such as fruit juice beverages. Typically, drink dispensers for fruit juice beverages prepare the beverages by mixing a concentrate product, such as orange juice concentrate, apple juice concentrate, etc., with water to provide a consumable drink product. In preparing such beverages, it is important that water and concentrate be mixed together in proper predetermined ratios to insure drink quality from one drink to the next. Such ratios typically range from 2:1 (2 parts water to 1 part concentrate) to 10:1. However, special problems arise in maintaining proper mixing ratios when dispensing fruit juice beverages as compared to soft drinks. Because fruit juice concentrates often include pulp and can have a relatively high and temperature dependent viscosity, it is difficult to directly measure the flow of fruit juice concentrate in the preparation of a drink, and it thereby is difficult to control the water to concentrate ratio of the beverage. In an effort to maintain desired ratios of water to concentrate, most fruit juice dispensers are designed to rely on a flow of concentrate delivered by a metering pump that is operated at a constant speed selected in accordance with a desired flow rate of concentrate, such as by a peristaltic pump that is driven at a constant speed, together with a delivery of water that is portioned into the concentrate at a constant flow of water, where the flow of water is selected in accordance with the desired flow of concentrate, thereby to provide what is intended to be a constant ratio of water to concentrate. These systems are of the open loop type, and therefore are unable to compensate for changes in the delivery rate of concentrate due to changes in the characteristics of the concentrate. Consequently, and as changes in concentrate temperature and attendant changes in concentrate viscosity cause variations in concentrate flow, even when a peristaltic pump is operated at a constant speed, conventional fruit juice dispensers are ill equipped to maintain a desired ratio of water to concentrate in the final drink product.